Security inspection technology and apparatuses are extensively applied in airports, railway stations, seaports and other important sites needing to carry out security inspection of persons' bodies. Known security inspection systems include a variety of concealed weapon detection (CWD) systems exploiting different physical principles to discover undesirable objects hidden under persons' clothing. Conventional security inspection systems currently in place at security checkpoints include metal detectors, X-ray systems and millimeter wave systems. However, metal detectors are prone to false alarms, and are not capable of detecting non-metallic objects. X-rays-based systems have deployment problems in view of their inherent radiation hazard and, also, are not able to detect certain materials/geometries (e.g. ceramic knives). As an alternative to existing systems, there have been proposed various microwave imaging systems having the ability to penetrate clothing to image concealed items.
Problems of microwave-based security inspection have been recognized in the conventional art and various techniques have been developed to provide solutions, for example:
US Patent Application No. US2008/0284636 discloses a method and apparatus for detecting objects when a person entering a secured zone is illuminated with low-power polarized radio waves. Differently polarized waves which are reflected back from the person are collected. Concealed weapons are detected by measuring various parameters of the reflected signals and then calculating various selected differences between them. These differences create patterns when plotted as a function of time. Preferably a trained neural network pattern recognition program is then used to evaluate these patterns without creating an image of the object and autonomously render a decision on the presence of a weapon or other object. An interrupted continuous wave system may be employed. Multiple units may be used to detect various azimuthal angles and to improve accuracy. The units may be used in a bi-static configuration which enables comparison of off-axis signals.
US Patent Application No. US2010/0220001 discloses a radar imaging system for capturing an image of an object within an area of interest through at least one visual impairment. The radar imaging system comprises at least one radar array. The radar array includes a plurality of transmitter elements and a plurality of receiver elements for receiving a plurality of coded return signals from an object through the at least one visual impairment. The system further comprises at least one processor coupled to the transmitter and receiver elements, which is adapted to transmit a plurality of differently coded signals toward the object and the at least one visual impairment; decode the plurality of coded return signals received by each of the receiver elements; extract from the decoded return signals a multiplicity of captured signals for each transmitter to receiver path; focus the multiplicity of signals on all points of interest within the area of interest by aligning the multiplicity of captured signals to be co-incident from a particular point within the area of interest; and sum the aligned signals to produce an image of the object.
US Patent Application No. US2012/0049863 discloses a method for detecting a covered dielectric object, where a microwave signal that can be modified in frequency is generated at a particular bandwidth and transmitted in the direction of the covered dielectric object. The microwave signal reflected by the object is then obtained from the three-dimensional measurement result in a lateral, two-dimensional pattern, a highest signal amplitude and a second-highest signal amplitude within a particular time period before or after the received microwave signal is identified in a plurality of pattern points of the pattern. The object is detected if an accumulation of pattern points of the pattern is present, in which the difference in each case between the highest and the second highest signal amplitude of the received microwave signal is less than a defined threshold value.
US Patent Application No. US2013/0082856 discloses a method and system for detecting the presence of subsurface objects within a medium. The imaging and detection system can operate in a multi-static mode to collect radar return signals generated by an array of transceiver antenna pairs that is positioned across the surface and that travels down the surface. The imaging and detection system pre-processes the return signal to suppress certain undesirable effects. The imaging and detection system then generates synthetic aperture radar images from real aperture radar images generated from the pre-processed return signal. The imaging and detection system then post-processes the synthetic aperture radar images to improve detection of subsurface objects. The imaging and detection system identifies peaks in the energy levels of the post-processed image frame, which indicates the presence of a subsurface object.
US Patent Application No. US2014/0341431 discloses a through-type of millimeter wave person body security inspection system, wherein a person to be inspected passes through an inspect passage therein for performing a security inspection. The disclosed security inspection system can make a total body dynamic scanning to the person to be inspected, and obtain millimeter wave images and optical images with respect to the person body, thereby achieving the inspection of prohibited articles hidden within clothing of the person body and an automatic alarm thereof.
US Patent Application No. US2015/0379356 discloses a system and method for detecting concealed weapons. A radiofrequency transmitter transmits an RF signal stream into a region of interest. An RF receiver receives a scattered signal stream from the region of interest. The scattered signal stream is generated in the region of interest from the radiofrequency signal stream when a target is at least partially within the region of interest. A plurality of resonant signal components are identified from the scattered signal stream. Preprocessed resonant signal components are generated by removing environmental signal components. A target assessment is determined from the preprocessed resonant signal components using a trained statistical model. A target response is triggered if the target assessment indicates that a weapon is detected on the target.
International Patent Application No. WO15/086524 discloses a method for capturing a 360-degree 3D view of the surface of a moving human or animal's body. The method comprises the steps of: (A) determining a speed of motion of at least one area of the body surface; and B) capturing at least said area of the body surface at a point in time when the value of the speed of motion of the area is lower than a defined threshold value.
The references cited above teach background information that may be applicable to the presently disclosed subject matter. Therefore the full contents of these publications are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.